A. Field of the Invention
This invention relates generally to magnetically activated circuit-breaker devices and, more specifically to magnetic armatures for such devices, including a spring-biasing means.
B. Description of the Prior Art
In electric circuit-breaker technology, it is known to use an electromagnetic-tripping means to cause instantaneous tripping of a breaker when current flow through the breaker exceeds a predetermined amount. Typically, the electromagnetic-tripping means will operate when current through the breaker exceeds the rated normal operating current for the breaker by a factor of ten or more.
In electric circuit-breaker device technology, it is also known to use a tripping means in the form of a a bimetallic member which becomes resistively heated by a current flowing through the breaker and which trips the breaker when current flowing through the breaker exceeds a predetermined amount. Typically, the bimetallic-tripping means will operate when current through the breaker exceeds the rated normal operating current for the breaker by a factor of two for a time period of 30 seconds to one minute, for example. Frequently, in circuit-breaker device technology, an electromagnetic-tripping means and a bimetallic-tripping means are used in combination.
Tripping arrangements for circuit breakers usually include a latch member for holding an actuating member of a switching arrangement of the breaker until the breaker is tripped by the latch member so as to unlatch the actuating member. The actuating member is then free to move under the action of a spring means contained in the switching arrangement so that previously closed contacts of the switching arrangement are rapidly opened.
In conventional electromagnetic tripping devices, a magnetic armature 10, such as the type illustrated in FIG. 1, is typically used to activate the tripping mechanism 12. As can be seen from FIG. 1, the magnetic armature provided therein includes a curved portion 14 which surrounds at least one half of the circumference of a guide post 16. A leaf spring 18 is attached to one end 20 of the magnetic armature 10 to maintain the other end 22 of the magnetic armature away from a magnetic yoke 24. When the current flowing through the circuit breaker exceeds a predetermined amount, the magnetic armature 10 is suddenly attracted to the magnetic yoke 24 and tripping mechanism 12 is disconnected from the magnetic armature 10 to cause the circuit breaker to open.
Another magnetic armature is described in U.S. Pat. No. 2,902,560 to Stanback et al. FIG. 1 of the above-noted patent illustrates that the magnetic armature is supported by the yoke, and a spring mechanism is attached to one end of the armature. One difficulty with using the magnetic yoke to support the armature is that the yoke and armature must be assembled together prior to installation within a circuit breaker housing. This greatly complicates the fabrication process of a circuit breaker and prevents easy replacement of the armature. FIG. 1 of U.S. Pat. No. 3,171,921 to Woods illustrates a similar magnetic armature as illustrated in the Stanback et al. patent.
Another type of magnetic armature used by others is illustrated in FIG. 1 of U.S. Pat. No. 4,156,219 to Coleman. This armature is of interest because it includes a spring-biasing means. The armature described therein, however, does not pivot but uses instead a series of vibratory forces to activate a latch mechanism.